'accelerated markedly' is correct and usable in written English.
You can use it to describe a rate of increase that is much greater than usual. For example, "After the introduction of the new policy, the company's growth accelerated markedly."
Investment accelerated markedly after a devastating earthquake on Taiwan in 1999.
The country's engagement with the developing world has accelerated markedly in the wake of the economic crisis.
Since 1995, however, productivity growth has accelerated markedly, about doubling the earlier pace, even after taking account of the impetus from cyclical forces.
While regional trade and integration endeavors in South Asia remained weak during the Uruguay Round, they accelerated markedly during the Doha Round.
Buoyed by a big pickup in public works spending and a Bank of Japan policy of flooding the economy with low-interest money, growth has accelerated markedly.
Early gains accelerated markedly in midmorning after Alan Greenspan, the Federal Reserve chairman, strongly suggested that the central bank would cut short-term rates if the economy's deceleration, already pronounced, threatened to become too rapid.
The risk is that the rate will accelerate markedly.
The July employment report does not signal that hiring from now on will accelerate markedly.
For copper, imports had fallen before the onset of the global crisis in August 2008, but they started accelerating markedly from February 2009 onward, again as the official P.M.I. was bullish at a time when the HSBC flash reading was bearish.
And, since 1981, the incidence among homosexuals has begun to accelerate markedly, according to the USC expert.
Preliminary evidence suggests that the contraction accelerates markedly at approximately age 65 years, after which 95% of the CD4+ T-cell diversity is lost (unpublished observations).
